Divergence of the diapause transcriptome in apple maggot flies: winter regulation and post-winter transcriptional repression

Abstract

The duration of dormancy regulates seasonal timing in many organisms and may be modulated by day length and temperature. Though photoperiodic modulation has been well studied, temperature modulation of dormancy has received less attention. Here, we leverage genetic variation in diapause in the apple maggot fly, Rhagoletis pomonella, to test whether gene expression during winter or following spring warming regulates diapause duration. We used RNAseq to compare transcript abundance during and after simulated winter between an apple-infesting population and a hawthorn-infesting population where the apple population ends pupal diapause earlier than the hawthorn-infesting population. Marked differences in transcription between the two populations during winter suggests that the 'early' apple population is developmentally advanced compared with the 'late' hawthorn population prior to spring warming, with transcripts participating in growth and developmental processes relatively up-regulated in apple pupae during the winter cold period. Thus, regulatory differences during winter ultimately drive phenological differences that manifest themselves in the following summer. Expression and polymorphism analysis identify candidate genes in the Wnt and insulin signaling pathways that contribute to population differences in seasonality. Both populations remained in diapause and displayed a pattern of up-and then down-regulation (or vice versa) of growth-related transcripts following warming, consistent with transcriptional repression. The ability to repress growth stimulated by permissive temperatures is likely critical to avoid mismatched phenology and excessive metabolic demand. Compared with diapause studies in other insects, our results suggest some overlap in candidate genes/pathways, though the timing and direction of changes in transcription are likely species specific.

Describing the Diapause-Preparatory Proteome of the Beetle Colaphellus bowringi and Identifying Candidates Affecting Lipid Accumulation Using Isobaric Tags for Mass Spectrometry-Based Proteome Quantification (iTRAQ)

“…Inspection of proteins significantly more abundant in the heads of diapause-destined females revealed several previously associated with increased stress hardiness including a putative small heat shock protein, a putative peptidoglycan recognition protein that could be involved in increased pathogen resistance, as well as glutathione S-transferase and thioredoxin, two proteins that have been implicated in ameliorating both oxidative stress and xenobiotic stress. Similar processes of increased hardiness to pathogens, oxidative stress and heat shock protein expression have commonly been found in other “omics” studies of insect diapause (Ragland et al, 2010; Poelchau et al, 2013; King and MacRae, 2015; Poupardin et al, 2015; Qi et al, 2015; Meyers et al, 2016 as some examples). Two proteins that stand out as being associated with development of synaptic activity in nervous systems, bruchpilot and syntaxin (Broadie et al, 1995; Wagh et al, 2006; Short, 2013), were also more abundant in diapause-destined females and have previously been associated with diapause in other insects and C. elegans worms (Ailion and Thomas, 2003; Ragland et al, 2011).…”

“…Increased stress hardiness is commonly a facet of diapause in many insect species and transcripts or proteins associated with stress hardiness have been identified in many studies (MacRae, 2010; Ragland et al, 2010; Poelchau et al, 2013; Poupardin et al, 2015; Qi et al, 2015; Meyers et al, 2016). Heat shock proteins in particular are associated with stress hardiness and are often highly expressed in diapausing individuals (Rinehart et al, 2007; Aruda et al, 2011; Pérez-Hedo et al, 2012; Lu et al, 2013; King and MacRae, 2015).…”

“…Previous studies of molecular mechanisms of diapause regulation have largely focused on the transcriptional level (Ragland et al, 2010, 2011; Poelchau et al, 2013; Qi et al, 2015; Kučerová et al, 2016; Meyers et al, 2016), with relatively few studies at the protein level (Zhang et al, 2012, 2013). Although proteins are the primary functional molecules in many different physiological processes, there is relatively little information on the differential expression of proteins across the phases of diapause.…”

Conceptual framework of the eco-physiological phases of insect diapause development justified by transcriptomic profiling

“…Since the publication of the pioneering paper of Denlinger and coworkers (29), a number of studies have described differences in gene transcription linked to insect diapause (20,(30)(31)(32)(33)(34)(35)(36). Indeed, some authors have attempted to integrate these studies and to detect commonalities in the diapause transcriptional profiles of different species, searching for the hypothetical genetic toolkit of diapause (18,19).…”

Standing geographic variation in eclosion time and the genomics of host race formation inRhagoletis pomonellafruit flies

“…Future studies are needed to identify the specific genes affecting eclosion time in R. pomonella, test for signatures of selection, and discern their demographic histories. In this regard, Ragland, Egan, Feder, Berlocher, and Hahn (2011) and Meyers et al (2016) showed marked differences between host races in gene expression patterns prior to diapause termination and suggested genes in the Wnt and TOR signaling pathways as candidate loci. Whole-genome DNA sequencing is also needed examine the apple race for soft vs. hard selective sweeps around candidate loci (Hermisson & Pennings, 2005), the former predicted under the standing variation hypothesis, while the latter is expected if new mutations enabled the shift to apple.…”